The invention is concerned with an attachment assembly to secure two membrane strips loosely laid parallel to each other and overlapping each other, in particular roofing membranes.
Flat roofs or roofs with small inclination angles are very often protected against rain penetration by loose-laid roofing membranes, mechanically secured against wind uplift. A very common and simple method consists of a pointwise attachment using attachment assemblies with, in general, a fastener screw and a load distribution plate in the edge region of the membrane. The next roofing membrane applied to the roof will then overlap the previous membrane and is secured to it by providing a water-proofing of the penetrated previous sheet. The water-proofed attachment of the two membrane strips in the overlap region may be achieved for PVC, EPDM or the like membranes by either hot gas welding or solvent welding. Rectangular, quadratic or circular load distribution plates are common as described in the patent applications EP-OS 0 283 184 and DE-OS 34 20 863.
The fastener screw of those attachments penetrates the load distribution plate in the center and is attached in the substrate on which the roofing membranes shall be attached. Profiled sheet metal is commonly used as a substrate. Symmetrical triangular plates are known for being used in the attachment of such materials as thermal insulation boards.
The sealing membrane in application such as those discussed above will billow under external wind action leading to a wind force on one side of the load distribution plate. This loading will tilt the load distribution plate around the edge of the load distribution plate pointing towards and parallel to the closer membrane edge. The symmetrical arrangement with a central penetration of the load distribution plate by the fastener screw leads to a force which will be approximately twice the applied wind force and which the screw has to transmit to the substrate.
Another disadvantage of the known symmetrical load distribution plates with central placement of the fastener screw is the relatively small pinching force, which the plate edge on the membrane strip.